In recent years, as a thickening agent for paints, cosmetics and the like, instead of the conventional polyacrylic acid-based thickening agent, a polyurethane-based thickening agent which is nonionic and is of a type that allows the viscosity to be increased by aggregation of hydrophobic groups has attracted attention.
Such polyurethane-based thickening agents are capable of allowing the viscosity to be increased by association of hydrophobic groups which the agents have at each terminal thereof. In addition, the agents are excellent in salt tolerance since they are nonionic, and have the advantage of being capable of imparting new rheological properties.
As the technique, it is known that the longer the chain length of a hydrophobic group present at the terminal is, the more enhanced the thickening effect is (Non-Patent Document 1).
As the polyurethane-based thickening agent, a material having three hydrophobic groups bound through a hydrophilic polyester group with a molecular weight of at least 1,500, wherein at least two groups of the hydrophobic groups are located at the terminal groups (Patent Document 1), and a material obtained by the reaction of:
(a) at least one water-soluble polyether polyol,
(b) at least one water-insoluble organic polyisocyanate,
(c) at least one monofunctional hydrophobic organic compound selected from a compound containing a hydrogen atom reactive with an isocyanate and an organic monoisocyanate, and
(d) at least one polyhydric alcohol or polyhydric ether alcohol (Patent Document 2, Patent Document 3) are known.
Moreover, a polyurethane-based thickening agent characterized by containing a monohydric alcohol with at least one other polar group or a trihydric alcohol as a polyhydric alcohol is also known (Patent Document 4).